This proposal concerns the use of mass spectrometry as applied to the analysis of the contents of single cells or parts of a cell (organelles). It will test various hypotheses about how different cells respond to external stimulation by electrical and chemical means. Much of the effort requires the combination of instrumentation that has never been so combined previously. Specifically, it will be necessary for this project to succeed to couple together microfluidic manipulations of cells on chips. Chemical separations of the contents of cells on chips the introduction of these contents into a mass spectrometer by means of an electrospray ionization interface, and the mass determination of the resulting ions using time-of-flight mass spectrometry whose data acquisition rate has been made sufficiently high that tiny amounts of sample can be recorded and analyzed.